In a scroll machine such as a pump, compressor or expander there is one basic coaction between the scroll elements in that one must orbit with respect to the other. The scroll element orbiting with respect to the other scroll element is generally called the orbiting scroll. In known designs both scroll elements are rotating, both are orbiting, one is fixed or is only capable of axial movement. A design where both scroll elements orbit, but at different radii, is exemplified by U.S. Pat. No. 3,874,827 which discloses a number of embodiments. Specifically, in FIG. 15, a version of a co-orbiting scroll design is disclosed in which two Oldham couplings are used. One is keyed between the scrolls but is located within the scroll elements. Basically, however, the disclosed embodiments have a driving major/orbiting scroll which has a fixed orbit and which drives a driven scroll which is able to move in a minor/smaller orbit as well as axially. The driven scroll is acted on by discharge pressure which forces the driven scroll into axial engagement with the driving scroll as well as a resilient material member which tends to locate the driven scroll at a position corresponding to the center of the minor orbit. The driven scroll moves in an orbiting motion subject to the bias of the resilient material which may make the orbit non-circular. In the disclosed embodiments, the compressor is of the open drive type with the motor above the scrolls.
In parent application Ser. No. 808,820, a method for dynamically balancing nested coupling mechanisms is disclosed. Basically, one coupling is keyed between the two scrolls and the other coupling is keyed between the driven or major scroll and the crankcase or fixed housing. The couplings can be arranged to provide a resultant centrifugal or inertial force which is easily balanced by a rotating counterweight.